Mother's Touch Can Alter Baby's Genes - Research

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Mother's Touch Can Alter

Baby's Genes - Research

By Anne McIlroy

The Globe and Mail

4-6-4

 

 

To an infant, a mother's touch is warm and comforting. Now a Canadian

researcher has found out how it can also trigger profound changes beneath

the skin -- how a caregiver's touch can physically alter a baby's genes.

McGill University's Michael Meaney's revolutionary findings may finally end

the long debate over whether heredity or the environment play the primary

role in shaping an individual's personality.

 

The nature-nurture debate has become less fierce in recent years: Many

scientists now accept that a mysterious dance between genes and environment

determines who we become. Dr. Meaney and his colleagues have uncovered an

important step in that dance, by showing for the first time how conditioning

can change the chemical structure of the genes we inherit -- in effect,

switching them on or off.

 

Their work is with rats. But his team has just begun a $4-million, five-year

study that could be the first in the world to confirm that it also applies

to humans.

 

There are two different kinds of rat mothers -- those that lick their pups a

lot and those that don't. Dr. Meaney found that, under provocation, the

high-licking mothers' offspring produced less of the stress hormone

cortisol. They are more stable individuals that are not as easily panicked.

 

Picture half a dozen rats in a cage, eating. Dr. Meaney claps his hands

loudly, and all the animals freeze. Some rats almost immediately go back to

gobbling their food, realizing that the researcher doesn't pose a real

threat. But others will remain immobilized for up to 10 minutes, and may

never go back their lunch. The difference? The timid rats are the offspring

of mothers who didn't lick them much.

 

How can licking make that much of a difference in personality -- is it due

to their genes, or the way they were raised? The answer is both. In essence,

the high-licking moms produce changes in their babies' DNA. Their pink

tongues somehow flick on the same chemical switch that turns genes on and

off in a developing embryo.

 

In the fetus, this process -- which scientists call methylation -- allows

development of the brain and organs to proceed in an orderly fashion. In the

baby rats, the high-licking mothers somehow switch on a gene that restricts

the production of cortisol. The low-licking mothers do not, so their pups

produce much higher levels of the stress hormone.

 

Cortisol helps prepare the body to deal with a threat -- such as the

possibility that a clapping researcher means them harm. In short bursts, it

can save an animal's life. But over the long term, a heightened stress

response has been linked to diabetes, heart disease, mental illness and

other serious ailments in both humans and lab animals.

 

" We have now studied that particular gene down to the level where we know

what maternal care is doing to turn it on or off, " says Dr. Meaney.

 

He sees his work as helping to reframe the nature-nurture debate, which

dates back to at least the 13th century. Extremists on one side have argued

that all animal behaviour is instinctive. Hard-liners on the other side have

taken the position that experience alone determines behaviour. The argument

flares every decade or so, most recently with the mapping of the human

genome. Now, the question is no longer whether genes are more important than

the environment, says Dr. Meaney. The question is how the environment

physically alters genes to produce individual differences.

 

The genetic changes in the baby rats affected not only the stress response

but also cognitive development, since high levels of cortisol inhibits the

growth of the hippocampus, a part of the brain involved in memory and

learning. Cortisol may also influence how well young animals pay attention.

Alison Fleming, a researcher at the University of Toronto, has found that

rats brought up without mothers -- and that don't have attentive researchers

stroking them with paint brushes to stimulate licking -- grow up with more

attention problems than animals that get that physical stimulation.

 

Could the same things be true in humans? We don't regularly lick our babies

or stroke them with paint brushes, and Dr. Meaney isn't suggesting that

anyone start. His hypothesis is that tactile contact has the same effect.

" Mothers don't lick their babies, but they hold them. And they probably

tickle them and touch them and stroke them and rub their hair. "

 

There is already indirect evidence that parental care influences how future

adults will respond to stress. In one study, young men and women who said

their mothers and fathers did a poor job in raising them became much more

stressed in an experiment designed to test how they react under pressure.

They were asked to perform rapid mental arithmetic problems, and a buzzer

would go off every time they were wrong.

 

Now Dr. Meaney and his number of colleagues across the country are looking

for evidence of genetic changes related to human parenting, from touching to

more subtle interactions. They want to know how parental care affects genes

in human babies.

 

Does the kind of parents you have influence your genes, causing you to

produce different amounts of the proteins involved in stress and learning

and behaviour? And do those changes make a major difference in children's

lives? Most intriguing to Dr. Meaney is the question of whether early damage

can be reversed.

 

To find answers, they are turning to a group of depressed and pregnant women

in Hamilton. Mothers suffering from severe depression often have trouble

bonding with the children and tend not to respond as quickly to their cues.

 

" Some don't bond, some don't bond well. Some of these moms will do the

instrumental things, but not the affectionate things. They will feed, bathe,

change [diapers]. But there is nothing on their faces, " says Dr. Meir

Steiner, a McMaster University researcher. " Some women are so irritable,

they cannot tolerate the behaviour of the baby, the noise, the crying. They

say they want to crawl out of their skin. "

 

In an ambitious experiment called the MAVAN project, for Maternal Adversity

Vulnerability and Neurodevelopment, Drs. Steiner, Meaney and others will

follow both the depressed mothers and a control group of healthy mothers

before they give birth, and closely monitor the moms and their children for

more than four years afterwards. The $4-million study is funded by the

Canadian Institutes of Health Research.

 

All of the depressed women will be offered treatment -- it wouldn't be

ethical to withhold it. But past studies have shown that a third are likely

not to respond. When the babies are born, they will be tested for 22 genes

that may make them vulnerable to aggressive or anti-social behaviour as well

as learning disabilities such as attention deficit disorder. Researchers

suspect these genes are affected by parental care. Their goal is to find out

whether a child with a genetic vulnerability and a depressed mother will get

into more trouble than a child with similar genes but with a healthy mother.

 

Researchers will monitor the children's cognitive and social development for

five years. They'll perform brain scans to monitor the physical development

of various brain regions. They'll also test the children's cortisol levels.

 

Most of the concrete data currently available about how a human mother

affects the development of her child come from prenatal studies, says

Stephen Matthews, a professor of physiology at the University of Toronto and

a lead investigator in the MAVAN

 

project. The most obvious example is fetal alcohol syndrome: Babies born to

mothers who drank heavily during pregnancy have smaller, less developed

brains.

 

Researchers also know that women who smoke, drink, are highly stressed or

are deprived of protein during pregnancy are more likely to give birth to

babies with low birth weights. These babies are more prone to a variety of

health problems, including high blood pressure, and are more at risk for

attention deficit disorder.

 

The second group that will be studied is in Montreal, selected from a group

of 5,000 children who took part in an earlier study on pre-term labour. Some

were born with low birth weights, while others were of average size. These

children will also undergo genetic tests. The researchers already have reams

of data about the mothers' pregnancies, and will go on to monitor how they

interact with their children.

 

These data should show, for example, whether low-birth-weight babies

genetically predisposed to attention deficit fare better with attentive

mothers than similar children whose mothers are less engaged.

 

New rat studies in Dr. Meaney's lab certainly offer hope that there will be

a difference. Researchers have found that poor maternal care means that a

number of genes in the brain involved in memory don't get activated. But if

you take those rats -- including those who are past puberty -- and put them

in an enriched environment, the genes are turned on.

 

" You really, literally can reverse it, " he says.

 

Not only that, but if you have a female rat pup born to a low-licking mother

removed to live with a high-licking surrogate mother, she will become a

high-licking mother when she grows up. On the other hand, if a high-licking

mother is subjected to high stress, she will pay less attention to her

offspring.

 

However, Dr. Meaney emphasizes that the consequences of less-attentive

maternal care may not always be bad. Dr. Meaney's theory is that the

low-licking rats are at the bottom of the social hierarchy, and as a result

lead more stressful lives. In this situation, helping offspring develop a

strong response to stress may be a good thing. For example, the extra

cortisol makes the animals less aggressive and so less likely to get into

fights. It may be nature's way of helping the animals adapt to their future

environment.

 

In human studies, researchers in Montreal have found that in poorer

neighbourhoods with high crime rates, the boys who don't get into much

trouble actually have higher levels of cortisol than boys who join gangs and

begin stealing cars. Their stress levels seem to make them more fearful and

less likely to partake in risky business.

 

There are many other examples in the natural world of organisms preparing

their offspring for the specific environmental challenges they will face.

Radishes that are harassed by caterpillars produce chemicals that are toxic

to the insects, and grow spines on their leaves. Plants that come from those

radishes' seeds will also have spiny leaves, and high levels of the toxic

chemicals.

 

" We are looking at something that happens pretty generally across all

biology, " says Dr. Meaney. " Nature didn't rip up the blueprint when it got

to us. "

 

Much remains unknown, but Dr. Meaney believes the mechanism he identified in

the gene that restricts cortisol production in rats is the same one at work

in all cases where a parent influences the expression of a gene. His work is

part of the burgeoning field of epigenetics -- the study of changes to

genetic material that don't involve altering the sequence of the four

nucleotides -- C, G, T and A -- that make up our genetic code.

 

" The whole world knows it really isn't just a question of genes, or just a

question of environment, " says Dr. Meaney. " It is the interaction between

the two of them. Fine, it makes sense intuitively, but what does it mean

when the environment interacts with the gene. How? That is what we are

showing. "

 

- Anne McIlroy is The Globe and Mail's science reporter.

 

Stress test Researchers have evidence that stress may actually start to harm

children in the womb. Among infants and toddlers, high and chronic levels of

stress can make learning more difficult, perhaps even shrinking the part of

the brain associated with memory. Stress may also make kids fat.

 

Experts say the following may be signs a child is unduly stressed. If the

problem persists more than a few weeks, medical assistance may be in order.

 

Physical problems: Stomach trouble, headaches or difficulty falling asleep

can be signs of childhood stress.

 

Worrying out loud: A stressed youngster may seek continual reassurance, and

ask parents repeatedly about hypothetical disasters (for instance, their

divorce or death).

 

Avoiding situations: If children don't want to go to class or shun

after-school activities, it may be because they find those environments

overly stressful. -- Anne McIlroy

 

Mother nature Can parents help their offspring adapt to the particular

environment they will face? Plants and animals do.

 

Radishes When infested by caterpillars; radish plants grow spiny leaves and

produce a natural insecticide. The seeds will produce radishes that already

have those defences.

 

Skink lizards If you expose a skink to the smell of its predators, a snake,

it will become hypersensitive to that smell. The offspring of that skink

will be four times more sensitive to the smell of snake than their skink

babies

 

Rats Rat pups born to mothers that do not lick them very much develop high

levels of the stress hormone, cortisol. Researchers suspect these rats are

born into a lower status in the social hierarchy and a strong stress

response may help them avoid dangerous confrontations.

 

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